The present invention relates to testing devices for fire detectors where the fire detector has at least one mode of activating the alarm which is resettable without replacement of the fire detector. The invention also relates to the cooperation between the testing device and the fire detector for selective energy transfer to the fire detector.
Fire detectors are well known and operate on several different modes. The simplest form of a fire detector is a fixed temperature fire detector which is designed to complete an electrical circuit once a certain temperature has been exceeded. In some cases the fire detector will be rated for a temperature of 135.degree. F. or possibly 180.degree. or 200.degree. F., depending upon its particular application. In addition to fixed temperature point fire detectors, fire detectors can also have a structure for sensing the rate of temperature rise. In a fire situation, the air temperature within the building or structure, subject to combustion, rises quite rapidly and this rapid rise in temperature can be sensed. For example, often fire detectors will be rated for a rate of rise of 15.degree. F. per minute. This is generally accomplished by having a variable volume pressure chamber with a control orifice which allows bleeding of the pressure such that the pressure in the pressure chamber is normally at atmospheric pressure. If for some reason the temperature of the room rapidly rises, the pressure within the pressure chamber will increase and force a diaphragm member to a distorted position where it closes an electrical circuit and completes the alarm. The control orifice is set or calibrated for a particular rate of rise. These rate of rise detectors are reusable in that if they sense a fire condition and activate the alarm, once the normal condition is returned or the rate of rise is no longer sufficient to hold the contacts together, the fire detector goes back to its normal position and will continue to operate and activate the alarm should a further rate of temperature rise be experienced. Such is not the case with some fixed point temperature sensing fire detectors where at a certain temperature a spring mechanism is released which closes the contacts and once so activated, the fire detector must be replaced.
Other fire detectors use a bi-metallic spring which moves at a given fixed point changing from concave to convex when sufficient heat is applied. Such fixed point detectors automatically reset when alloed to cool.
The testing of fire detectors having two activation mechanisms, one of which is reusable, has been accomplished in the past, however they generally rely on the heating of the air about the fire detector where the energy is transferred to the fire detector primarily by convection or convection in combination with radiation. These devices have not configured the heating source in a manner to concentrate or focus radiate energy on a particular surface of a fire detector and, in general, the entire unit has been equally heated by convection.
Prior art testing devices would include lighters used by technicians in the field, electrical light bulbs which heat the air and cooperate with a housing to provide a closed envelope of air about a fire detector with this envelope not only heating the collection fin of the fixed point temperature, but the housing of the fire detector which would have a pressure chamber therewithin. In some cases, the use of electric light bulbs, such as a 100 watt bulb, has been used and a glob of heat resistant material has been applied to the end of the bulb to isolate the surface temperature of the bulb at that point from the fin. The surface of the light bulb is very high and the normal configuration of the light bulb would be such to generally position this hot surface very close to the collection fin.
Hair dryers and hot water sponges have also been used to raise the temperature of a fire detector for testing purposes.
One can appreciate that it is important to periodically test a fire detecting system if possible and certainly this is possible where the activating mechanism is reusable once brought to the activation point. It can also be appreciated that care must be exercised to ensure, in fire detectors which have dual systems, one of which is not reusable, that the mechanism which is not reusable is not activated during the testing of the device.
The fire detectors basically rely on energy being transferred to the fire detector to heat the fire detector and, when appropriate, activate the same. The rate of rise actuation can operate at a much lower temperature in that it is looking for the rate of temperature change as determined by a change in pressure within the pressure chamber. In testing of a rate of rise fire detector, it is important to apply heat to the fire detector in a manner that the one time fixed temperature sensor does not become activated. It is desirable that the heat be monitored to allow the user to discontinue the test prior to reaching the activation point of the fixed temperature.